Field of the Invention
The invention relates to a method for controlling a motor vehicle drive train, in which the direction of rotation of the drive train is determined by evaluating sensor signals from a first sensor unit which is provided on the output side of the drive train and which includes a sensor wheel fastened to a rotatable component of the output side of the drive train and two rotational speed sensors which are provided circumferentially adjacent to one another, fixedly with respect to the housing, at an effective distance from the sensor wheel and are connected to an evaluation unit via signal lines. The evaluation unit determines the direction of rotation of the drive train from codirectional edge changes of the sensor signals. A safety and comfort function is activated and deactivated as a function of the determined direction of rotation of the drive train, a distinction being made between the rotational or driving states of a clockwise rotation of the drive train according to a forward movement of the motor vehicle, a counterclockwise rotation of the drive train according to a reverse movement of the motor vehicle and an undetected direction of rotation of the drive train according to a vehicle standstill or to an undetected vehicle movement.
The invention relates, furthermore, to a device for controlling a motor vehicle drive train, with a first sensor unit for determining the direction of rotation of the drive train, the first sensor unit including a sensor wheel fastened to a rotatable component of the output side of the drive train and two rotational speed sensors which are provided so as to be circumferentially adjacent to one another, fixedly with respect to the housing, at an effective distance from the sensor wheel and are connected to an evaluation unit via signal lines and through the use of which the direction of rotation of the drive train can be determined from codirectional edge changes of the assigned sensor signals.
Sensor units for determining the rotational speed of a rotatable component have been known for a long time. For example, sensor units of this type in an automated motor vehicle transmission are assigned in each case to a transmission shaft and are used for controlling the gear shifting or controlling the ratio of a transmission control, or in a motor vehicle are assigned in each case to a wheel hub and are used for the braking control of an antilock or traction control system. These are in this case usually magnetoelectric or inductoelectric rotational speed sensors which are provided in each case in the effective range of an assigned sensor wheel fastened to a rotatable component and in the event of a rotation of the sensor wheel generate a pulse signal or square wave signal which is transmitted via a signal line into an evaluation unit and is evaluated there into rotational speed information. The sensor wheel is usually configured as a toothed disk with a spur toothing, on which the assigned rotational speed sensor is arranged in the effective range of the spur toothing in an essentially radial orientation and fixedly with respect to the housing.
However, with a sensor unit of this type, only the amount of the rotational speed of the respective component can be determined, not the direction of rotation of the component. However, as is known, for example, from Published, Non-Prosecuted German Patent Application No. DE 30 41 041 A1, this is possible in a relatively simple way in that two rotational speed sensors are arranged in the effective range of a sensor wheel so as to be circumferentially adjacent to one another, in which case the time sequence of the pulses or of the codirectional edge changes, that is to say edge changes taking place in the same order, of the respective sensor signals can be evaluated in order to determine the direction of rotation of the respective component.
A drive train, which has transmission units or gear units with a tooth flank backlash or clearance, such as a pair of gearwheels of the selected gear of a manual transmission and a differential, and elastic components, such as a vibration damper of an engine clutch and a hardy disk, is, in principle, an oscillatory system. Consequently, during operation, torsional vibrations and the bridging of tooth flank clearance occur, which may lead to local changes in the direction of rotation. So that an unequivocal determination of the direction of rotation of the drive train can nevertheless be carried out, according to the prior art several codirectional edge changes have to be awaited when the sensor signals are evaluated in the evaluation unit, thus adversely leading to a time delay in the determination of the direction of rotation, and this possibly resulting in at least losses of comfort on account of a delay in the activation and deactivation of safety and comfort functions.